The present invention relates to an exhaust gas system with a gas sensor, in particular with a particle sensor.
In order to be able to sense the concentration of soot in the exhaust gas of vehicles having internal-combustion engines, particle sensors are used which are arranged in a pipe element (exhaust gas pipe) of an exhaust gas system.
Company-internally, BMW examined the flow conditions at a particle sensor arranged in an exhaust gas pipe of an exhaust gas system. The examined sensor arrangement is schematically illustrated in FIGS. 1A, 1B.
FIG. 1A shows a gas sensor or particle sensor, which projects into the interior of an exhaust gas pipe 2 having a center longitudinal axis 3. In the exhaust gas pipe 2, an exhaust gas volume flow mexhaustgas flows in a flow direction 4. A flange 5 is arranged in the wall of the exhaust gas pipe 2. The flange 5 has a passage opening provided with an internal thread 6. The gas sensor or particle sensor 1 has a housing 7, which has a threaded housing portion 8 provided with an external thread and screwed into the passage opening or into the internal thread 6 of the flange 5.
As illustrated in FIG. 1A, an annular gap 9 is provided between a radial exterior side of a forward section of the threaded housing portion 8 and an interior circumferential section of the passage opening projecting into the interior of the exhaust gas pipe 2, which passage opening is provided in the flange 5.
A partial volume flow (gap flow) mgap of the exhaust gas volume flow mexhaust can enter into the annular gap 9 and flow around the housing 7 or the threaded housing portion 8 of the particle sensor 1. As a result of the annular gap 9, the flow around the particle sensor is relatively strong, which leads to a drop of the pressure gradient between an exhaust gas input 10 and an exhaust as output 11 of the particle sensor 1. By way of the exhaust gas input 10, a partial volume flow msensor enters into the particle sensor 1, and, by way of the output 11, exhaust gas flows from the particle sensor 1 back into the exhaust gas pipe.
A good flow through the particle sensor takes place only if the pressure difference between the input 10 and the output 11 is sufficiently high, which is a prerequisite for good measuring results. When this “rinsing gradient” is reduced, a smaller mass flow will flow at a lower local velocity through the particle sensor, whereby less exhaust gas and fewer particles arrive in the sensor, which has an unfavorable effect on the functionality of the sensor.
The present invention begins precisely at this point.
It is an object of the invention to create an exhaust gas system with a gas sensor arranged therein, particularly with a particle sensor arranged therein, which is optimized with respect to the exhaust gas flow conditions such that measuring results can be achieved that are as good as possible. In particular, the flow around the particle sensor, which impairs the rinsing gradient, is to be kept as low as possible.
This and other objects are achieved by an exhaust gas system having an exhaust gas pipe, through which exhaust gas flows in one flow direction, which exhaust gas pipe has a pipe wall. In the pipe wall, a flange is arranged, which has a passage opening provided with an internal thread. A gas sensor is screwed into the passage opening. In particular, the gas sensor may be a soot particle sensor which is provided, for example, for sensing the concentration of soot particles contained in the exhaust gas. The gas sensor has a threaded housing portion provided with an external thread, which threaded housing portion is screwed into the passage opening.
An annular gap (which is required for the purpose of manufacturing) is provided between a radial exterior side of a forward section of the threaded housing portion and an interior circumference section of the passage opening of the flange, which interior circumference section projects into the interior of the exhaust gas pipe.
It is the core of the invention that the flange has a “flow guiding element”, which extends along a downstream partial circumference of the threaded housing portion, and which is provided for limiting or largely preventing an exhaust gas flow in the annular gap.
The flow guiding element may be designed similar to “half a fender of a bicycle” or to “half a sleeve”. It is the purpose of the flow guiding element to create an “obstacle” for the flow around the particle sensor. By means of the flow guiding element, the flow around the particle sensor is reduced, and the rinsing gradient between an exhaust gas input and an exhaust gas output of the particle sensor is enlarged. As a result of the correspondingly larger pressure gradient, a greater exhaust gas mass flow will occur through the particle sensor, whereby its measuring quality will be improved.
The invention can be constructively implemented in a very simple and cost-effective manner.
According to a further development of the invention, a radial gap is present between the flow guiding element and the downstream partial circumference of the threaded housing portion.
It has been mentioned that the flow guiding element extends over a partial circumference of the threaded housing portion. The partial circumference or circumferential region may, for example, be between 150° and 210°, of the total circumference or between 160° and 200° or between 170° and 190°. The flow guiding element preferably extends over a circumferential area of essentially or exactly 180° of the threaded housing portion.
According to a further development of the invention, the flow guiding element has, in the region of its front-side end, i.e. in the area of its end facing the interior of the exhaust gas pipe, a section projecting radially to the interior toward a center longitudinal axis of the gas sensor or particle sensor. This section, at least to an extent, covers a partial circumference of the front side of the threaded housing portion of the gas sensor or particle sensor.
Between the section of the flow guiding element projecting radially toward the interior and the front side of the threaded housing portion, a space or a small gap may exist—viewed in the direction of a center longitudinal axis of the gas sensor or particle sensor.
The flange, into whose passage opening the gas sensor or particle sensor is screwed, can be welded into the wall of the exhaust gas pipe or can be connected with the exhaust gas pipe in a different fluid-tight manner.
According to a further development of the invention, a partial section of the threaded housing portion of the gas sensor or particle sensor projects by at least a distance beyond a front side of the flange facing the interior of the exhaust gas pipe.
The gas sensor or particle sensor may have a sleeve-type head. The sleeve-type head, in turn, has a center longitudinal axis and projects beyond the flow guiding element in the direction of the interior of the exhaust gas pipe.
The exhaust gas inlet of the gas sensor can be formed by an annular inflow gap or an inflow gap present between the threaded housing portion and the sleeve-type head. By way of this inflow gap, exhaust gas can flow into the housing of the gas sensor.
The sleeve-type head of the gas sensor—viewed in its circumferential direction—has at least one passage, by way of which exhaust gas, which has entered the housing of the gas sensor, can flow farther into the interior of the sleeve-type head.
According to a further development of the invention, the gas sensor has a sensor element, which is arranged in the center in the sleeve-type head or which projects into the sleeve-type head. Exhaust gas entering the sleeve-type head flows along the sensor element to a front-side opening of the sleeve-type head. The front-side opening forms an exhaust gas output of the gas sensor, by way of which exhaust gas flows back into the exhaust gas pipe.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.